1. Field of the Invention
This invention relates, generally, to sanitization devices and wastewater treatment systems for use on board mobile vessels, and particularly to such devices and systems for use on boats and ships.
2. Prior Art
Mobile vessels such as motor vehicles, aircraft, and watercraft, especially those of larger size, are often equipped with a toilet. Of late there has been a greater emphasis on treatment of wastewater from these on-board toilets, known as heads. Some regulatory measures have been implemented which severely restrict the bodies of water into which watercraft can discharge untreated wastewater and other types of liquid discharge.
Other regulations allow discharge into certain bodies of water, but the effluent discharged must meet certain treatment standards.
The increased regulation and the desire of watercraft owners and operators to minimize the environmental impact of the discharge from their vessel have led to the development of various Marine Sanitation Devices (MSDs). Current Coast Guard regulations discuss three classes of MSDs. Type I MSDs treat sewage with chemicals or by other means prior to discharging the treated wastewater from the vessel. Type I MSDs must meet certain standards for the discharge and the discharge can have limited visible floating solids. Type II MSDs operate similarly to Type I MSDs but must meet higher treatment standards. A Type III MSD is simply a holding tank.
The disadvantage of having only a holding tank (a Type III MSD) is that the vessel is severely restricted as to where it can discharge the untreated wastewater. Generally, the vessel will have to be on the high seas to discharge the untreated waste or will have the holding tank pumped out. Unauthorized discharges can result in serious penalties for the vessel operator.
Vessels up to and including those 65 feet or greater in length may use Type I, II, or III MSDs. Vessels 66 feet and over must have a Type II or Type III MSD. Because Type II MSDs are typically bigger and more expensive, and because they generally require more power than Type I MSDs, Type II MSDs are not commonly found on vessels 65 feet and smaller.
Type I devices include those which use the salinity of the water and electrical current to make hypochlorous acid (chlorine), which then treats the sewage. These devices require salt water in order to operate. If used in fresh water, such as that found in many inland lakes and streams, the operator must add salt to the device. Other disadvantages of these devices are their bulk and the large amount of power necessary to operate them.
Another Type I MSD is a system in which the wastewater is flowed through a cartridge which contains a solid chlorine tablet. The tablet dissolves as the wastewater is treated. A further disadvantage of the electric current and chlorine cartridge systems discussed above is that they are limited to treating a single "flush" batch at a time. Neither of these Type I MSDs typically has any holding capacity.
Other Type I systems do have the capacity to hold more than one flush. However, the operator must carry and resupply the chemicals necessary for treatment of the wastewater in the tank.
What is needed is a Marine Sanitation Device which overcomes the shortfalls of the devices which are currently known in the art.